A method of locating a mobile station is provided. In the present invention, the mobile station is capable of communicating with at least three base stations, each having at least two antennas. To estimate the location of the mobile station, the distance between the mobile station and each base station is calculated based on the time of arrival (TOA) of a mobile station signal at the base station, a first estimated MS location area is defined as an overlap area of circles of which the radiii are the distances between the MS and the base stations. Then, the location of the mobile station is estimated based on the time of signals received through the two antennas of each base station and based on the angle between the antennas of each base station and the mobile station. Here, the angle is calculated from the phase difference between the received signals and a communication frequency of the signals. A second location area is defined as an area defined by lines connecting the base stations to the mobile station. Then, the MS is determined to be located in a common area of the first and the second location areas.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for locating a mobile station (MS) capable of communicating with at least three base stations (BSs) each having at least two antennas, comprising the steps of: (a) calculating the respective distance between said MS and said each BS based on a Time of Arrival (TOA) method using an MS signal arriving at said each base station; (b) determining an overlap area, defining a first estimated MS location area, by an intersection of circles with each radius of said circles corresponding to said calculated distance between said MS and said each BS; (c) estimating the location of said MS based an Angle of Arrival method(AOA), defining a second estimated location area, wherein said AOA method includes the steps of: (c)(i) receiving time of signals received through two antennas of said each BS; (c)(ii) estimating the MS location based on an angle between said each antenna of said each BS with respect to said MS, wherein said angle is calculated from the phase difference between the received signals and a communication frequency of the signals; and (c)(iii) estimating said second location area defined by the lines connecting said each BS to said MS based on said AOA method; and, (d) determining a new location of said MS defined by a common area of said first location area and said second location area.
2. The method of claim 1 , wherein said step of estimating said first location comprises the steps of: calculating the respective distance between said MS and said each BS based on said MS signal arriving at said each BS; drawing the respective circle using said calculated distance between said MS and said each BS as respective radius with respect to said each circle; and, estimating said overlap area of said three circles as said first location area.
3. The method of claim 1 , wherein said step of estimating said second location area comprises the steps of: calculating a coarse Angle of Arrival (AOA ( )) between said MS and said antennas of said each BS based on a Time Difference Of Arrival (TDOA) of said signals received through said two antennas; estimating a plurality of AOA values between said MS and said two antennas of said each BS using a phase difference of said signals received and a communication frequency; and, determining an AOA most approximate to said calculated coarse AOA among said plurality of said estimated AOA values as a final AOA value.
4. The method of claim 3 , wherein said time difference ( T) is calculated by the following equation: T = K max F s wherein F s representing a sampling frequency in digital conversion is F s and K max representing a correlation peak which is represented by R ( s 1 , s 2 ) [ k ] = - m m s 1 [ n ] s 2 [ n - k ] , wherein s 1 n and s 2 n represent converted sample digital values converted from said received signals at said respective antenna, m representing the maximum length of s 1 and s 2 , and represents the number of samples of the maximum length of s 1 and s 2 .
5. The method of claim 4 , wherein said coarse AOA ( ) is calculated by the following equation: = sin - 1 ( 2 c 2 t 1 t 2 ( s - ct 1 ) ( s - ct 2 ) ( s - D ) ) wherein c represents the speed of light, ct 1 represents the distance between said MS and one of said antennas of said BS, ct 2 represents the distance between said MS and said another antenna, and D represents the distance between said two antennas.
6. The method of claim 5 , wherein in said phase difference ( ) is calculated by the following equation: = 1 n n = 1 n ( s 1 [ n ] , s 2 [ n ] ) wherein s 1 n and s 2 n represents the converted sample digital values converted from said received signals at said respective antenna, (s 1 n , s 2 n ) represents said phase difference between s 1 n and s 2 n , and n represents the number of samples of the maximum length of s 1 and s 2 .
7. The method of claim 1 , wherein said MS signal comprises an RTD (Round Trip Delay) signal for communicating between said MS and said each BS.
8. The method of claim 1 , wherein said MS signal comprises a PUF (Power Up Function) signal for communicating between said MS and said each BS.
9. A system for estimating the location of an MS in a CDMA mobile communication system, comprising: at least three BSs, each having two different antennas spaced a part by a predetermined distance, for calculating a Time of Arrival (TOA) based on an MS signal received at said each BS, for calculating a Time Difference of Arrival (TDOA) and a phase difference of signals arriving at said two antennas of said each BS, and for determining a final Angle of Arrival (AOA) between said MS and said two antennas of said each BS based on said calculated TDOA, said phase difference, and a communication frequency of said MS; said MS capable of communicating with said three BSs; a location data processor for estimating a first MS location area and a second MS location area using an MS signal arriving at said each BS and for determining a common area of said first MS location area and said second MS location area; and, wherein said first MS location area is determined using a Time of Arrival (TOA) method and said second MS location area is determined using an Angle of Arrival (AOA) method, and wherein the location of said MS is defined by a common area of said first MS location area and said second MS location area.
10. The system of claim 9 , wherein said each BS comprises: a demodulator for demodulating two RF signals received through said antennas of said BS to baseband signals; an analog-to-digital converter for converting said demodulated baseband signals into digital values; a signal processor for calculating said TDOA and said phase difference of said converted digital values; a coarse AOA calculator for calculating a coarse AOA based on said calculated TDOA; an ambiguous AOA estimator for estimating a plurality of AOA values based on said phase difference of said converted digital values; and, an angle ambiguity resolver for determining said final AOA by determining an estimated AOA most approximate to said coarse AOA among said plurality of said estimated AOA values.
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March 13, 2000
October 1, 2002
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